linux-kernel - Re: [PATCH] vfio/type1: Use follow

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Date:   Fri, 12 Feb 2021 15:08:51 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
CC:     <cohuck@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <pbonzini@...hat.com>,
        <peterx@...hat.com>
Subject: Re: [PATCH] vfio/type1: Use follow_pte()

On Fri, Feb 12, 2021 at 12:01:50PM -0700, Alex Williamson wrote:
> follow_pfn() doesn't make sure that we're using the correct page
> protections, get the pte with follow_pte() so that we can test
> protections and get the pfn from the pte.
> 
> Fixes: 5cbf3264bc71 ("vfio/type1: Fix VA->PA translation for PFNMAP VMAs in vaddr_get_pfn()")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index ec9fd95a138b..90715413c3d9 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -463,9 +463,11 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
>  			    unsigned long vaddr, unsigned long *pfn,
>  			    bool write_fault)
>  {
> +	pte_t *ptep;
> +	spinlock_t *ptl;
>  	int ret;
>  
> -	ret = follow_pfn(vma, vaddr, pfn);
> +	ret = follow_pte(vma->vm_mm, vaddr, NULL, &ptep, NULL, &ptl);
>  	if (ret) {
>  		bool unlocked = false;
>  
> @@ -479,9 +481,17 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
>  		if (ret)
>  			return ret;
>  
> -		ret = follow_pfn(vma, vaddr, pfn);
> +		ret = follow_pte(vma->vm_mm, vaddr, NULL, &ptep, NULL, &ptl);

commit 9fd6dad1261a541b3f5fa7dc5b152222306e6702 in linux-next is what
export's follow_pte and it uses a different signature:

+int follow_pte(struct mm_struct *mm, unsigned long address,
+              pte_t **ptepp, spinlock_t **ptlp)

Recommend you send this patch for rc1 once the right stuff lands in
Linus's tree

Otherwise it looks OK

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason